Many applications use methods and systems for position determination, e.g. of a geodetic instrument, a vehicle or the like, which are based on global positioning systems, such as, for example, GPS, GLONASS or the European Galileo system. These Global Navigation Satellite Systems (GNSS) are based on the reception of satellite signals.
The requirements of vehicle guidance or navigation, e.g. in agricultural, mining, trucking or railroad applications, have subtle differences to those of surveying, including a much stronger requirement for continuously available positioning. However, the ability to provide continuously available positioning is impaired when there is poor satellite “visibility” or one or more of the satellites are inoperative, which results in the accuracy of the position determination being degraded. For example, GPS systems require at least four satellites to be “visible” to enable precise position determination.
It is well known in the art to integrate positioning measurements from GNSS data with data from one or more vehicle-mounted Inertial Navigation Systems (INS) to provide improved position determination systems and methods with high reliability, availability, accuracy and integrity. Such systems are commonly referred to in the art as Integrated Navigations Systems.
An INS provides the position, velocity, orientation, and angular velocity of a vehicle by measuring the linear and angular accelerations applied to the system in an inertial reference frame.
In many Integrated Navigation Systems, Kalman Filters are used to generate an estimate of a trajectory and to allow vehicle guidance in real-time. A Kalman Filter is a recursive estimator that relies on an estimated state from a previous step and current measured data to calculate an estimate for a current state along with an explicit measure of confidence in this estimate.
As such, Integrated Navigation Systems require post processing of both the GNSS data which, in a GPS system, occurs on the output from the GPS receiver, and the positioning data obtained from the INS to provide positioning information.
In this specification, the terms “comprises”, “comprising”, “includes”, “including” or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.